MATERIAL HANDLING—TRANSPORTATION OF SOLIDS 95 Where, C = Constant = 0,780 for roller flights, = 0.933 for shoe nights, - W = Load handled in tons per hour, L = Length of conveyor in feet, and H = Elevation in length of conveyor in feet. The multiplicity of standards and the differing spacing of flights makes an accurate formula for ascertaining cost a difficult matter, but for all practical purposes for approximate estimates of relative cost Formula (13) will be iound sufficiently reliable. RCfc == (0.0115A + 0.0516VJ + 7)L + #vT Formula (13) Where, A = Area of flights in square inches—width times length, L - Length of conveyor in feet, and K = Constant = 1.5 for shoe flights, = 3.0 for roller flights. Depreciation varies greatly in the case of flight conveyors as both the flights and the trough are subject to severe abrasive action, by the material with which they are in contact in operation. Virtually every material varies in its destructive action. With Formula (14), depreciation factors for some of the materials commonly handled by flight conveyors are given. ED/C = ((0.00323A + 0.00237VT + 1.075)L + 0.6\/J)F Formula (14) Where, F = Depreciation factor = 0.47 for coke 0.99 for ashes 1.00 for fine coal 1.06 for lump coal, run-of-mine 1.15 for lime and cement 1.50 for sand and gravel 1.60 for ore (average) 1.80 for crushed stone 1.83 for broken stone (coarse) Fixed charges for flight conveyors may be taken, as in the case of belt conveyors, at 8.5 per cent per year, but in addition there is an annual renewal charge amounting to about 20 per cent of the initial cost. Labor expense, though no higher per ton than that of belt conveyors, is considerably more on account of the necessary attention to gates, etc., per foot of conveyor and is usually about 3 cts. per inch width of conveyor, irrespective of the load handled or the length of the conveyor. Flight conveyors owing to their heavy consumption of power arc much more limited in length than are belt conveyors. Incidental expenses for supplies, etc., vary closely with the power requirements and are somewhat heavier in the case of shoe-flight conveyors, being for roller-flight conveyors about 2 cts. per horsepower per hour and for shoe flights about 2.25 cts. per horsepower per hour. The respective net costs of operating the two types of flight conveyors differ to some extent, as will be noted in the following example. Example.—Required the net operating cost per ton of a 100-ft. flight conveyor handling 120,000 tons of sand and gravel during 800 operating hours in the year. The conveyor to be inclined about 3 deg. (5.25 ft. in its length). Power to command a value of 3 cts. per horsepower delivered at conveyor drive. Costs wanted for both shoe- and roller-flight conveyors.